What makes a Rallycross tyre?

A rallycross tyre needs to have several elements to cope with the demands placed on it. It needs a pattern that conforms to the technical regulations and a compound suitable for both gravel and asphalt surfaces. It needs a complex construction that gives unrivalled performance with the strength to take the punishment that these surfaces give when tackled with a 600BHP car. Unsurprisingly, this isn’t easy!

Patterns

All homologated rallycross tyres must feature a “tread” pattern that complies with a specific set of regulations as approved by the FIA. Cooper’s ACB11 Rallycross tyre was developed from a range of rallycross slick tyres to conform to these regulations which state that between 17% and 25% of the tyre must be a pattern or “void”; this is often referred to as the “land to sea ratio”. Intended mostly for use in the dry, the ACB11 has another trick up its sleeve. It was designed to allow additional grooves to be hand cut into the pattern to turn it from a ‘dry’ to an ‘intermediate’ and finally a ‘wet’. More grooves disperse more water and this three-stage cutting process allows teams and drivers to tailor the tyre’s pattern to the conditions. Cooper has also added a 17” full RX race wet for the RX Championship. This has been developed especially for this season’s European Rallycross Championship.

Compound

Cooper’s rallycross compounds have been tested and developed over many years to provide the best performance for events that take place from chilly Scandinavia to the warmth of Southern Europe, Brazil and the USA, with many varying track layouts and surfaces. The range has needed to evolve alongside changing cars and sporting regulations over two decades, starting with products for rear-wheel drive, front-wheel drive and then four-wheel drive. Typically a rallycross compound will work at 90°C on mixed surfaces but the compound will happily go up to 120°C in hotter conditions or on tracks that are mostly paved.

Construction

To give the compound and tread pattern the platform they need to perform, each Cooper rallycross tyre is hand built, using the best materials available to give drivers the best product possible. This involves laying multiple layers of Kevlar and nylon in the tyre sidewalls to give strength and flexibility in the tyre. Tyres are designed to respond to a driver’s needs, while being able to withstand the enormous loads applied when landing from huge jumps and riding razor-sharp kerbs. The tyres can withstand a lot of punishment but you will occasionally see a “deflation”, usually after a car has just gone a little too hard over a jump or played bumper cars with another driver! Often a deflation is the result of the wheel cracking or the valve being snapped off during impact.

Testing

Cooper has always worked to give drivers the quickest and best tyres possible with more than 20 years of continuous testing and development under its belt. To stay ahead in a competitive tyre market the Company’s on-going development team regularly tries new compounds and constructions in private tests, working with teams to create tyres that allow rallycross stars to compete flat-out for lap after lap in one of the world’s toughest and most spectacular forms of motorsport.